This invention relates generally to an apparatus and method for rodent control and in particular it relates to apparatus and method using ultrasonic sound waves to repel or disperse rodents such as rats and mice.
The dispersion of rodents by use of ultrasonic sound waves generally is performed by producing sound waves at frequencies of about from 15 to 30 KHz, frequency modulating the sound waves by sweeping them through the frequencies of this band and amplitude modulating the sound waves asynchronously with the frequency modulation of same. This provides ultrasonic energy at frequencies which the rodents are sensitive to with the randomization of the amplitude modulation preventing the rodents from adapting themselves to the ultrasonic energy.
Rodent control systems using such apparatus and methods generally are placed in areas of rodent infestation to drive, scatter or disperse the rodents from such areas. Such systems are required to be small in size and consume small amounts of electrical energy to produce the ultrasonic sound waves. Several such systems are known with an example of such system being that of that described in U.S. Pat. No. 3,636,559.
In U.S. Pat. No. 3,636,559 an ultrasonic sound signal is swept through a range of frequencies at which rodents are sensitive with an amplitude modulation of the ultrasonic sound waves occurring asynchronously with the frequency modulation. In addition, the sound waves are alternatively turned on and turned off to provide an interrupted output which permits the system speaker to cool off. In one embodiment of that patent, a plurality of speakers are provided which are sequentially operated to provide the ultrasonic sound levels so that one or more of the speakers may be cooling off while the others are operating. It should be noted that the system such as is disclosed in U.S. Pat. No. 3,636,559 operates with an ultrasonic sound level output by the speaker of about 100 decibels.
The power consumption required of such a system to produce the ultrasonic sound levels normally required to disperse the rodents may be reduced by providing negative feedback damping to a tuned band-pass filter output circuit of such a system. A reduced power consumption provides for smaller, less expensive system power supplies, smaller, more convenient packaging and less wasted heat which must be dissipated from the system.